Explosive particles coated with a water-soluble ionic dye

ABSTRACT

ENHANCED FLOW PROPERTIES ARE EXHIBITED BY NONCAKING PARTICULATE HIGH EXPLOSIVE MATERIALS HAVING A COATING OF AN IONIC DYE ADSORBED ON THE SURFACE OF THE EXPLOSIVE PARTICLES.

3,682,725 EXPLOSIVE PARTICLES COATED WITH A WATER-SOLUBLE IONIC DYE Cornelius James Noel Kelly, Simsbury, Conn., assignor to The Ensign-Bickford Company, Simsbury, Conn. No Drawing. Filed Apr. 30, 1969, Ser. No. 820,639 Int. Cl. C(l6b 19/02 U.S. Cl. 149-9 9 Claims BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates generally to high explosive detonating material. More particularly, it is concerned with the production of free-flowing high explosives suitable for use in the manufacture of devices such as detonating cord and the like.

Particulate high explosive material as received from the supplier, such as pentaerythritol tetranitrate (PETN), is generally a recrystallized solid initially formed as a fine grist having a low stability level until recrystallized. The recrystallization operation can be adjustable to produce particles having substantially different size distributions; however, regardless of size distribution the particulate explosives generally exhibit relatively poor flow properties. This is true despite the fact that most detonating explosives are nonhygroscopic and are not subject to caking or setting, as is the case with materials such as ammonium nitrate. In order to overcome the relatively poor flow characteristics, it has been suggested that fine particulate explosives be treated with a bonding or cementing material to form flowable agglomerated granules capable of being broken apart after completion of the flow operation.

Since the tendency of the explosive material not to flow freely through narrow openings is believed to be due at least in part to induced electrostatic charges, it has been suggested that the explosive may be beneficially atfected by suitable chemical treatment, such as rinsing with an antistatic agent. The presence of a static charge is perhaps best evidenced by the tendency of the material to collect at the small perforations provided in the charging plate for a detonator charging machine and by the accumulation of particles around the periphery of an orifice through which the particles are flowing. This accumulation of particles generally occurs in a continuous manner thereby reducing the flow through the orifice and eventually resulting in complete blockage thereof. As indicated in US. Pat. No. 3,320,847 issued May 23, 1967 to Kelly et al. and entitled Method of Manufacturing Explosive Devices, the antistatic agents conventionally used heretofore to combat this condition have been saturated long chain or fatty alcohol sulphates.

Accordingly, it is an object of the present invention to provide a new and improved class or group of antistatic agents for particulate high explosive materials, which agents impart enhanced flow properties to the explosive materials treated therewith.

Another object of the present invention is to improve the flow properties of noncaking, high explosive materials by adsorbing on the discrete particles thereof a surface coating which reduces the tendency of the particles to accumulate electrostatic charges and at the same time permits clear identification of the treated material.

3,682,725 Patented Aug. 8, 1972 A still further object of the present invention is to provide particulate explosive material of the type described having an adsorbed surface coating of an ionic antistatic material differing substantially from the fatty alcohol sulphates employed heretofore, the antistatic material being adapted for quick and simple application and being effective in providing a percent or more improvement in the flow properties over that of untreated material.

Still another object of the present invention is to provide a new and improved method of enhancing the flow properties of noncaking, particulate explosive material of medium fine and coarser particle size without adversely affecting the materials sensitivity to initiation.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

These and related objects are accomplished in accordance with the present invention by treating the noncaking or nonsetting particulate high explosive materials, such as PETN, with a solution of an ionic dye in which the explosive is substantially insoluble to enable the dye to be adsorbed on the surface of individual explosive particles, and subsequently removing excess dye solution and drying the treated explosive.

A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENT The improvement in flow properties effected in accordance with the present invention may be quantitatively determined by measuring the flow rate of the particulate explosive material through an orifice of standardized size and configuration. For this purpose it has been found that a circular orifice having a diameter of 0.125 inch is particularly well suited for determining the effect of antistatic agents on the flow characteristics of those particulate explosive materials conventionally employed in the manufacture of detonating cord and the like. In the particular test apparatus employed, a short thimble or sleeve, which tapers inwardly at its lower end toward a bottom opening or orifice of appropriate size, is fixedly positioned below a substantially larger supply hopper. The orifice is closed and a known amount of the particulate material usually grams or more, is placed in the hopper, the exit opening of the hopper being positioned within the thirnble so that the particulate material only partially fills the thimble. The circular orifice is opened and the time required for the full amount of material to flow therethrough is measured, the flow being stopped after about 3 minutes if the full charge of 150 grams has not passed through the orifice.

Using this technique it has been found that coarse, noncaking high explosives as received from the supplier, such as cap grade PETN, generally have a flow rate of about 0.5 gram per second and less. Additionally, such material invariably tends to accumulate at the edge of the orifice indicating the presence of electrostatic charges on the explosive. However, when the explosive is treated in accordance with the present invention, the flow rate exhibits an increase of 100 percent and more with no noticeable accumulation of material at the orifice.

As mentioned hereinbefore the dry particulate explosive material used in accordance with the present invention is preferably a material which is nonhygroscopic and is not subject to caking or setting upon storage under ambient environmental conditions. The high explosive is usually an organic material of the detonating type and, in accordance with the preferred embodiment, exhibits little or no solubility in the solvent of the antistatic agent.

The explosive pentaerythritol tetranitrate (PETN) has found wide commercial application in the manufacture of detonating cord and is generally preferred, although other materials of a similar type may be employed. For example, other high explosive materials which may be used in accordance with the present invention include cyclotrimethylene trinitramine (RDX), cyclotetramethylene trinitramine (HMX), lead azide and nitromannite. Although explosives such as trinitrotoluene (TNT) and lead styphnate also exhibit beneficial flow properties after treatment in accordance with the present invention, the adsorption of the antistatic agent by these materials is less uniform and requires repeated application for best results.

The particle size distribution of the high explosive material treated in accordance with the present invention may vary although materials of medium fine and coarser grade give the best results. Generally, the super fine material is not appreciably benefitted by the use of the antistatic treatment of the present invention since the maximum particle size of such material is generally less than about microns. Accordingly, the invention finds its most beneficial application when used on coarser explosive material, such as cap grade, which generally conforms to the following screen analysis (U.S. Standard Sieves):

Retention on mesh screen1% maximum Retention on 50 mesh screen-35% minimum Pass through 100 mesh screen-20% maximum However, the beneficial elfect is evidenced on finer, high explosive materials than cap grade, for example, where about percent of the material or more has a maximum dimension of at least about 150 microns. Thus, materials exhibting a particle size distribution comparable to that possessed by the dormant or partially active fuses described in the aforementioned US. Pat. No. 3,320,847 may be advantageously treated in accordance with the present invention. Similarly acceptable results may be obtained with medium fine explosives having the following particle size distribution (U.S. Standard Sieves):

Retention on mesh screen-1% maximum Retention on mesh screen5% maximum Retention on mesh screen20% maximum Pass through 325 mesh screen-25% minimum In accordance with the present invention the particulate high explosive material is rinsed or soaked in a dilute solution of the antistatic agent for a short period of time after which the excess solution is removed and the explosive is dried to reduce its moisture content to about 0.2 percent by weight. The concentration of the antitatic agent in the solution generally is less than 5.0 percent by weight with the preferred range being from about 0.1 to 1.0 percent by weight. However, it will be appreciated that the repeated use of a more dilute solution may provide the beneficial results of the present invention while concentrations of 5 or 10 percent or more also may be used. It has been found that increasing the concentration of the antistatic agent does not appear to provide a comparable increase in the flow characteristics of the material and therefore a solution of 1 percent and less usually is preferred. It will, of course, be appreciated that the primary requisite is the adsorption of a thin surface coating of the antistatic agent on the explosive material to provide the desired antistatic characteristics. Accordingly, the concentration actually used will vary with the material on which it is to be adsorbed as well as with the particular antistatic agent without departing from the spirit of the present invention.

The antistatic agents utilized in accordance with the present invention are water-soluble ionic dyes. Although a predominant number of the dyes found most effective are classified as basic dyes, some acidic dyes such as Anthraquinone Green GNN (color index 61570) have also been effective in improving the flow rate of high explosives treated therewith. Among the basic dyes, that is, those dyes wherein the organic portion thereof is cationic in character, it has been found that the organic cations having a quaternary ammonium group or radical appear to give the best results and are therefore preferred. Examples of these basic dyes include those whose common name and structure are set forth in Table I.

TABLE I Name Structure Malachite Green N(CH3) 2C1 TABLE IContinued Name Structure Methyl Green"; I?(OH3)2OZH5BI Auramin O- -27.;212: 17(CH3) a Rhodamine EGDN- O H5CZHN (CzH5) C1" H30 Cy CH3 O0 0 0 02m (02mm more):

the,

\1 Sold under the trade name "Sevron by E. I. du Pont de Nemours & Company. b Structure unknown but categorized as a basic dye of the methine type having a structure believed to be similar to that shown.-

It is another feature of the present invention that many For example, it is known that untreated PETN and RDX of the ionic antistatic dyes not only improve the flow rate have a heat stability of more than 16 hours as measured of the high explosives but do so without adversely affecting the stability or sensitivity of the explosive material. 75

by the Abel Heat Test. Although the heat stability of explosives appears to be reduced when the basic dye employed contains radicals selected from the group consisting of primary and secondary amino radicals, pyridinium nitrogen and carboxylic acid radicals, the same is not true for acid dyes such as Anthraquinone Green GNN (color index 61570). Examples of the basic dyes which do not reduce heat stability are Malachite Green, Brilliant Red 4G and Brilliant Red B.

The invention is further illustrated by the following detailed examples in which percentages by weight are utilized.

EXAMPLE I The particle size distribution of a supply of cap grade PETN was found to be as follows:

Retained on 50 mesh screen-76.4% Retained on 100 mesh screen-12.9% Retained on 200 mesh screen-7.9% Pass through 200 mesh screenl.8%

Using the flow rate test equipment described hereinbefore with a circular orifice having a diameter of 0.125 inch, the flow rate of this PETN was found to be less than 0.5 gram per second. About 150 grams of this explosive was allowed to soak for to minutes in an 0.5 percent by weight solution of Malachite Green dye (color index 42000), after which it was filtered and dried to a moisture content of 0.2%.

The flow rate of the explosive thus treated was measured under identical flow conditions to those used for the untreated material. The treated material exhibited a flow rate of 1.1 grams per second. Thus, it can be seen that a 100 percent improvement in the flow rate of the explosive particulate material was imparted by the adsorption of the ionic dye on the explosive material.

The heat stability of the explosive as measured by the Abel Heat Test was found to be greater than 16 hours for both the untreated and dye treated material. Thus, the antistatic treatment was effective in improving the flow of the explosive without adversely affecting its stability.

EXAMPLE II RDX having a particle size distribution of 17.9 percent retained on a 50 mesh screen, 74.6 percent retained on a 100 mesh screen, 4.4 percent on a 200 mesh screen and the remainder (3.1 percent) passing through the 200 mesh screen was treated with an 0.5 percent aqueous solution of Rhodamine SGDN dye (color index 45160) in substantially the same manner as described in Example I. The treated explosive material was filtered, dried and tested for flow rate. The flow rate of the treated material was found to be 1.1 grams per second as compared with a flow rate of less than 0.5 gram per second for the same material before treatment.

EXAMPLE III In order to study the effect of dye concentration on the flow rate of explosives, the procedure of Example I was repeated using the same supply of PETN and 4 different dye solutions at various dye concentrations. As can be seen from the following table, the flow rate is not substantially enhanced by an increase in the dye concentration above about 0.5 to 1.0 percent by weight.

8 The individual PETN samples treated with an 0.5 percent aqueous solution of Brilliant Red 4G and an 0.5 percent aqueous solution of Brilliant Red B were tested for heat stability in accordance with the Abel Heat Test. Both samples had a stability of more than 16 hours.

EXAMPLE IV The procedure of Example I was followed using PETN having the following particle size distribution:

Retained on 20 mesh screen1.1% Retained on 50 mesh screen39.8 Retained on mesh screen42.3 Retained on 200 mesh screen-12.6% Pass through 200 mesh screen-4.2%

Separate samples of the particulate high explosive were treated with different solutions of Auramin O dye. The resultant flow properties are set forth in the following table:

The procedure of Example I was repeated except that the Malachite Green was replaced by the dyes indicated. The following table lists the dyes and the flow rates obtained after treatment of the explosive.

TABLE IV Flow rate (grains per Dye second) Anthraquinone Green GNN (color index G1570) 1.1 Methyl Green (color index (42590) 1.1 Basic Fuchsia (color index 42510) 1.1 Janus Green B (color index 11050) 0.9

As can be seen from the foregoing detailed description, treatment of high explosive particles with dilute ionic dye solutions enhances the fiow properties thereof. Additionally, appropriate dyes have no adverse effect on the heat stability of the explosive treated therewith.

As will be apparent to persons skilled in the art, various modifications and adaptations of the foregoing specific disclosure can be made Without departing from the underlying principles and teachings of the present invention.

I claim:

1. A fiowable granular material comprising solid discrete particles of a nonhygroscopic high explosive compound selected from the group consisting of cyclotrimethylene trinitramine and pentaerythritol tetranitrate having an adsorptive coating of an antistatic agent comprising an water soluble ionic dye in an amount sufficient to reduce the susceptibility of the particles to the accumulation of induced electrostatic charges and improve the flow characteristics of the particles.

2. The composition of claim 1 wherein the explosive includes pentaerythritol tetranitrate particles having an average particle size of at least 10 microns and a maximum particle size substantially greater than 100 microns.

3. The composition of claim 1 wherein the coated explosive particles have a heat stability substantially equal to that of the particles prior to coating.

4. The composition of claim 1 wherein the explosive particles are substantially water insoluble and the dye is a water-soluble salt of a basic dye.

5. The composition of claim 1 wherein the dye is a basic organic compound free of radicals selected from 9 the group consisting of primary amino, secondary amino, pyridinium and carboxylic acid radicals.

6. A process for improving the flow properties of nonhygroscopic high explosive particles selected from the group consisting of cyclotrirnethylene trinitramine and pentaerythritol tetranitrate comprising the step of treating said particles with a dilute solution of an ionic dye to effect adsorption of the dye on the surface of the explosive particles.

7. The process of claim 6 wherein the dye solution has a dye concentration of about 5.0 percent by weight and less.

8. The process of claim 6 wherein the dye solution has a dye concentration of about 0.1 percent to about 1.0 percent by weight.

9. The process of claim 6 wherein the solution is an aqueous solution of a basic dye.

References Cited UNITED CARL D. QUARFORTH, Primary Examiner 15 S. J. LECHERT, 111., Assistant Examiner US. Cl. X.R. 

